This is not a step by step guide to how to do this, my intention is to provide a summary of the process, and a confirmation to anyone that is going to try this procedure that I was able to do this successfully. Please note that this can damage your DVD and mean that you will have to replace it with a new one. I take no liability for anyone who tries this unsuccessfully, this is purely a case study of someone who has done this successfully.
Note that making my drive region-less was a two stage process 1) Install the region-less firmware onto the DVD drive, then 2) Install software to update the DVD software to be region-less.
My hardware setup is a Powerbook G4 12 inch with a Matshita DVD-R UJ-816 with firmware DXJ3 installed. My drive was region locked to the US, as I had changed the region more than 5 times. The information contained in this article only applies to this hardware setup. Note that it was accidently region locked to US region after experimenting with playing DVDs of European and US regions, all I wanted to do was play my European discs again.
a) The instructions and downloads can be found at: http://www.powerbook-fr.com/dossiers/dvd_region_free_en_article30.html
b) Warnings can be found at: http://superdrive.cynikal.net/
More instructions are found within the disc image when you download it.
At powerbook-fr.com (a) I found the firmware download called "firmware_uj816_XXJ3.dmg.zip". Note that it is XXJ3 not DXJ3, the X indicates the firmware is the regionless version. After unzipping the firmware the disc image opens giving two files. I read the "READ THIS" file which informed me to plug in my Powerbook into the mains and close all applications and also to disconnect from the internet. I then ran the "UJ-816 XXJ3" program, following the on-screen prompts. I then got a dialog which gave me an "update" button. Whilst doing this I did nothing else on the computer and ran no other applications. I then clicked the "Update" button. A progress bar went across the screen and the text changed rapidly. This took a number of minutes to get to about 95% complete, then progress slowed down a lot, and the text now changed at a slower rate. I then got the message that "an extra 5 seconds is required" then in about 10 seconds progress completed and I was informed that the installation was successful and that the computer needed restarting. I then clicked on the restart button on the dialog. On restarting my computer I confirmed that the drive was still functioning correctly by entering a photo CD. The next step was to get the DVD player software modified to be region-less.
I clicked on "latest version" to download the latest version of Region X. I then unzipped the file and ran the program. I then got a dialog warning me that my drive must be region-less/region unlocked for Region X to work. I said OK and then selected region 2 with 4 changes remaining to allow me to use European discs again.
I can now play European DVD's again, horah!